Currently flexible plastic components are attached to rigid plastic by use of an adhesive, by friction fitting and/or by mechanical locking means. The current method for adhesive bonding, where a flexible plastic component is adhesively bonded to a rigid plastic, has the disadvantage that when the flexible plastic is stretched or compressed a shear stress develops between the rigid plastic and the flexible plastic component. This shear stress causes a gradual shearing of the adhesive at the interface between the rigid plastic and the flexible plastic component.
Friction fit, and/or the mechanical lock means can loosen from the strains resulting from the stretches and/or compression of the flexible plastic component.
Thus there is a need for a new method of permanently affixing a flexible plastic component to a rigid plastic component that reduces the likelihood of the flexible component becoming separated from the rigid plastic component.
The present invention relates to a method of attaching a flexible plastic. Flexible plastic as considered for this application, will include flexible plastics and either rubbers or artificial elastomers. Rigid plastics are thermoplastics and thermosetting plastics. The present technique can be used for such purposes as retrofitting suction cups into rigid plastic tubes such as the legs on children's bathtube seats.
A flexible plastic component is attached to a rigid plastic component in accordance with the present invention by adherence to the following procedure: (a) a passage is provided in the ridig plactic component; (b) an extension is provided to the flexible plastic component; (c) the extension is contoured to slidably engage the passage in the rigid plastic; (d) the extension is provided with one or more indentations; (e) and rigid plastic inserts are contoured to fit the indentations so that when the inserts are positioned in the indentations the extension, in combination with the inserts, will slidably engage the passage provided in the rigid plastic. When affixing the flexible plastic to the rigid plastic the inserts are placed into the indentations; the inserts are wet with a bonding liquid; the extension in combination with the inserts is engaged into the passage and the extension maintained in the position for a time sufficient to allow the inserts to bond to the passage. The bonding liquid can be an adhesive or a solvent.
It is preferred that the rigid plastic inserts have the same composition as the rigid plastic and that the bonding liquid be a solvent which will soften the rigid plastic inset and the material on the inside surface of the passage in the proximity of the inserted insert. In this manner the insert will be permanently bonded to the rigid plastic passage.
In a preferred embodiment the passages and the associated extensions have volumes generated by displacing a line parallel to and about an axis. The surface of the volume is then provided with indentations which preferably are channels substantially normal to the axis of generation.
In one particular embodiment of the extension is a cylinder with a circular channel having its center on the axis of generation.
It is further preferred that the plastic inserts art provided with recession in which fluid such as the bonding liquid, and any gas that may be entrapped and compressed in the tube can flow. These recesses are preferably between about 0.001 inch and 0.010 inch. The recesses should be so disposed as to enhance the wetting of the inside surface of the rigid plastic passage by the bonding liquid.
In another preferred embodiment the inserts have beveled edges and the inserts, when placed into the channels form a press fit with the passage and provide pressure between the inserts and the passage while the bonding liquid is developing a bond between the passage and the inserts.
In another preferred embodiment means are provided for retaining the inserts in the channel. These means can be either a friction fit between the channel and the inserts or, alternatively, pins and pin receivers can be used.
The channel geometry is preferable such that the depth of the channel is approximately 0.25 times the diameter of the protrusion. Furthermore it is preferred that the depth of the protrusion is no greater that the distance between the channel and the end of the protrusion.